The most common way to determine if a person is overweight or obese is to calculate body mass index (BMI). BMI is an estimate of body fat based on comparing a person’s weight to his or her height.
Health care providers also look at BMI, along with information about additional risk factors, to determine a person’s risk for developing weight-related diseases. Usually, the higher a person’s BMI, the higher the risk of disease.
An adult’s BMI can be determined using a BMI calculator. Health care providers use BMI ranges to indicate a person's weight status. For adults, a BMI of:
It is important to remember that although BMI is generally a good way to estimate how much body fat a person has, it does not measure body fat directly and therefore is not reliable in all cases. For example, a person may weigh extra because he or she is athletic and has a lot of muscle, and not because he or she has excess body fat.
For children age 2 and older and for teens, BMI uses weight and height, but adds sex and age into the calculation. Instead of using a specific number like the BMI charts for adults, the BMI for children and teens is listed as a percent. This percentage indicates a child’s BMI in relation to the BMIs of other children of the same sex and age. A child and teen BMI calculator can provide a BMI.
Children age 2 and older are considered:
Body fat can be measured in other ways in addition to BMI, including waist circumference, calculation of waist-to-hip circumference ratios, measuring the thickness of a skinfold (a pinch of skin and fat), and techniques such as ultrasound that are more precise than BMI. A health care provider can help determine if such tests are necessary.
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